(a) Field of the Invention
The present invention is related to an electronic musical instrument wherein a musical sound is produced by computing the amplitudes of respective partial components of an aimed musical sound waveshape at successive sample points of the musical waveshape and by converting these computed amplitudes to a musical sound, as the computations of the amplitudes are carried out.
(B) Description of the Prior Art
U.S. Pat. No. 3,809,786 entitled COMPUTER ORGAN discloses an electronic musical instrument wherein the amplitudes at successive sample points of a musical sound waveshape aimed are computed and then converted to a musical sound as the amplitude computations are carried out. In this instrument, a discrete Fourier algorithm is implemented to calculate the individual harmonic component amplitudes at each sample point, using a stored set of harmonic coefficients which characterize the resultant waveshape. For each sample point, the amplitudes of plural harmonic components are calculated individually by multiplying the coefficient associated with each harmonic component by a sine value related to the sample which value is read out from a sinusoid table memory. The instrument includes means for programmatically scaling the harmonic coefficients as a whole with lapse of time to obtain such sound amplitude transient effects as the attack and decay effects, and so forth. However, it contains no means for changing the individual harmonic coefficients, independently of each other, with time lapse to obtain a tonal quality variation characteristic of the resultant musical sound with respect to time. Therefore, this prior art instrument is not able to produce a musical sound much realistically simulated to that of the most natural musical instruments of which tonal quality will change slightly with the lapse of time.
Another prior art electronic musical instrument of the type described, which is capable of producing a musical sound whose tonal quality varies with time lapse, is disclosed by Japanese patent application No. 49-111818 (Laid-open on Apr. 15, 1976 under the laying-open No. 51-43912). This instrument is so designed that the individual harmonic coefficients are varied individually with lapse of time, causing the relative amplitudes of the respective harmonic components, i.e., the tonal quality of the resultant musical sound to change with time. The harmonic coefficients are calculated at a high speed by a calculating device as the amplitude calculations are carried out, as described below referring to FIG. 1. The amplitudes for each sample point of an aimed musical waveshape are calculated at regular time intervals T.sub.1, and hence, if 16 harmonic components, for instance, are evaluated in the calculation of the amplitude, the calculation for each harmonic component must be accomplished in a time interval T.sub.2 = T.sub.1 /16, which is usually a relatively short period of time. This prior art instrument is arranged so as to accomplish the calculation of each harmonic coefficient at such a short time interval T.sub.2, which leads to the accompaniment by a difficulty in implementing the harmonic coefficient calculation. In other words, an expensive high-speed calculating device is required for calculating the harmonic coefficients, resulting in a higher cost of the instrument as a whole.